Line illuminator and image reader incorporating it

ABSTRACT

A line-illuminating device which is resistant to shrinkage problems caused by repetition of heating and cooling includes a white casing made of polycarbonate or the like, a light guide made of an acrylic resin or the like and accommodated in the casing such that the light-emitting surface thereof is exposed, and light-emitting elements (for example, light-emitting diodes) as a light source provided on both ends of the casing so as to abut against the end surfaces of the light guide without a gap. The casing is divided into two portions in the longitudinal direction, and a gap is formed between the two divided portions. With this gap, even if the light guide shrinks due to repetition of heating and cooling, the divided portions can effectively shrink together with the light guide via the gap, and the abutting state between the end surface of the light guide and the light-emitting element can be maintained.

TECHNICAL FIELD

The present invention relates to a line-illuminating device and acontact-type image-scanning device (image sensor) in which theline-illuminating device is incorporated.

BACKGROUND ART

A contact-type image sensor is used as a device for scanning a documentin a facsimile machine, a copying machine, an image scanner or the like.The contact-type image sensor is provided with a line-illuminatingdevice for linearly illuminating a document surface along a mainscanning field. In the line-illuminating device, a bar-shaped lightguide is accommodated in a casing, light from a light source (LED) isintroduced into the bar-shaped light guide, and the light is allowed toreflect within the bar-shaped light guide and be emitted from alight-emitting surface along the longitudinal direction of thebar-shaped light guide toward the document surface, in which thelight-emitting surface is exposed from the casing (Patent Documents 1and 2). There have been known a type in which a light source is providedon one end of the casing, and a type in which light sources are providedon both ends of the casing.

[Patent Document 1] Japanese Patent Application Publication No. 8-163320

[Patent Document 2] Japanese Patent Application Publication No.10-126581

Among the conventional line-illuminating devices, as for the type inwhich a light source is provided on one end, the light amount isinsufficient, and the illumination intensity is non-uniform along themain scanning direction. Thus, a light-scattering pattern is provided.However, it is still difficult to completely solve the problem ofnon-uniformity.

In contrast, as for the type in which light sources are provided on bothends, a problem is caused by thermal expansion. Specifically, while thetemperature of the contact-type image sensor rises to quite a hightemperature at the time of driving, it is cooled to around a roomtemperature at the time of stopping. The material of the casing istypically polycarbonate, and the material of the light guide is acrylic.Therefore, relative expansion and shrinkage repetitively occur betweenthe casing and the light guide due to the difference in the thermalexpansion coefficient. This results in the light guide shrinkagecompared to the casing, which causes a gap between the end surface ofthe light guide and the light source, and part of light generated by thelight source unpreferably leaks.

DISCLOSURE OF THE INVENTION

In order to solve the above-mentioned problems, according to a firstaspect of the present invention, light sources are provided on both endsof a casing of a light-illuminating device, and the casing is divided,for example, into two portions in the longitudinal direction.

By providing a gap between the two divided portions of the casing, whenthe light guide expands or shrinks, the casing correspondingly expandsor shrinks, whereby the light source can be kept abut against the endsurface of the light guide.

The divided portions may be apart from each other. However, if they areslidably engaged with each other, it is possible to prevent light fromleaking from the light guide.

According to a second aspect of the present invention, light sources areprovided on both ends of a casing of a light-illuminating device, andthe light source is pressed against the end surface of the light guidewith an elastic member which is formed integrally with the casing.

In this instance, it is preferable that the end of the light guide beprojected from the end of the casing in an estimated amount ofshrinkage.

According to a third aspect of the present invention, a light source isattached to a casing on one end of a casing of a light-illuminatingdevice in the same manner as the conventional art, and another lightsource is attached directly to the end surface of the light guide.Incidentally, the light sources may-be attached directly to the endsurface of the light guide on both sides.

As a method for attaching, there is a method in which a raised portionis provided on the end surface of the light guide and the light sourceis engaged with the raised portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an image scanning device in which aline-illuminating device according to the present invention isincorporated;

FIG. 2 is a perspective view of the line-illuminating device accordingto the present invention;

FIG. 3 is an exploded perspective view of the line-illuminating device;

FIG. 4 is a sectional view of the intermediate portion of a casing;

FIG. 5 is a similar view to FIG. 4 showing another embodiment;

FIG. 6 is a view showing a main part of another embodiment in which anelastic member is provided in the casing; and

FIG. 7 is a view showing a main part of another embodiment in which alight-emitting element is attached directly to the light guide.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be describedwith 25 reference to the accompanying drawings. FIG. 1 is a sectionalview of an image scanning device in which a line-illuminating deviceaccording to the present invention is incorporated, FIG. 2 is aperspective view of the line-illuminating device according to thepresent invention, FIG. 3 is an exploded perspective view of theline-illuminating device, and FIG. 4 is a sectional view of theintermediate portion of a casing.

As shown in FIG. 1, an image scanning device is comprised of a frame 1having recessed portions 1 a and 1 b, a line-illuminating device 10provided in the recessed portion 1 a, a sensor substrate 4 with aphotoelectric transducer element (line image sensor) 3 attached to therecessed portion 1 b, and a rod lens array 5 for unit magnificationimaging which is held within the frame 1. A glass plate 2 is providedabove the frame 1. Light emitted from a line-emitting surface 11 a ofthe line-illuminating device 10 is directed to a document G through theglass plate 2, the light reflected on the document G goes to the rodlens array 5 and is detected by the photoelectric transducer element(line image sensor) 3 so as to scan the document G. The frame 1 is movedwith respect to the glass plate 2 in a sub-scanning direction, so that adesired area of the document G can be scanned.

As shown in FIG. 2, the line-illuminating device 10 is comprised of awhite casing 12 made of polycarbonate or the like, a light guide 11 madeof an acrylic resin or the like and accommodated in the casing 12 suchthat the light-emitting surface 11 a is exposed, and light-emittingelements (for example, light-emitting diodes) 13 as a light sourceprovided on both ends of the casing 12 so as to abut against the endsurfaces of the light guide 11 without a gap.

The bottom surface of the light guide 11 is provided with a lightscattering pattern 11 b for allowing the light emitted from the lightsource to scatter. The light scattered by the light scattering pattern11 b is emitted from the light-emitting surface 11 a.

As shown in FIG. 3, three pins P1, P2, and P3 are formed on the end ofthe casing 12. The pin P1 and the pin P2 are located in an oppositeposition with respect to each other, and the pin P1 and the pin P2 havethe same diameter. The pin P3 is located adjacent to the pin P1, and thediameter of the pin P3 is smaller than that of the pin P1 and the pinP2.

On the other hand, the light-emitting element 13 is provided with threeholes H1, H2, and H3 corresponding to the three pins, respectively. Thehole H1 and the hole H2 correspond to the pin P1 and the pin P2,respectively, and the hole H3 corresponds to the pin P3, which meansthat the diameter of the hole H3 is smaller than that of the other holesand the pin P1 and the pin P2 cannot enter the hole H3. Consequently,coupling of the pin to the wrong hole can be prevented.

As shown in FIG. 4, the casing 12 is divided into two portions in thelongitudinal direction, and a gap 14 is formed between the two dividedportions 12a. With this gap, even if the light guide 11 shrinks due torepetition of heating and cooling, the divided portions 12 a shrinktogether with the light guide 11, and the abutting state between the endsurface of the light guide 11 and the light-emitting element 13 can bemaintained.

FIG. 5 is a similar view to FIG. 4 showing another embodiment. In thisembodiment, the left and the right divided portions 12 a are engagedwith respect to each other so as to prevent the light guide 11 frombeing exposed.

In another embodiment shown in FIG. 6 using a unique attachmentstructure of the light-emitting element 13, the end surface of the lightguide 11 and the light-emitting element 13 can be prevented from beingseparated due to the difference in the thermal expansion coefficient.Specifically, an elastic member 15 is formed integrally with the end ofthe casing 12, so that the light-emitting element 13 can be pressedagainst the end surface of the light guide 11.

In this embodiment, the light guide 11 is projected from the end of thecasing 12 in an estimated amount (t) of shrinkage of the light guide 11.

In another embodiment shown in FIG. 7, a modified attachment structureof the light-emitting element 13 is used. In this embodiment, no pin isprovided in the casing 12. Instead, the pins P1, P2 and P3 are providedin the light guide 11, and the light-emitting element 13 is attacheddirectly to the end surface of the light guide 11. In these embodimentsshown in FIGS. 6 and 7, the above-mentioned attachment structure may beused only on one end of the light-illuminating device, and aconventional attachment structure may be used on the other end.

INDUSTRIAL APPLICABILITY

As mentioned above, according to the present invention, in theline-illuminating device comprising the casing and the light guide whichare made of a different material, since the casing is divided into twoportions in the longitudinal direction, the light-emitting element ispressed against the end surface of the light guide with the elasticmember all the time, or the light-emitting element is attached directlyto the end surface of the light guide, even if heating and cooling arerepeated a plurality of times and the light guide shrinks compared tothe casing, the abutting state between the light-emitting element andthe end surface of the light guide can be maintained and light can beintroduced into the light guide effectively.

1. A light-illuminating device comprising: a casing; a transparent lightguide accommodated in the casing; and light sources provided on bothends, in the longitudinal direction of the casing, in which light fromthe light sources is introduced into the light guide, the light isreflected within the light guide and introduced in the longitudinaldirection, and is allowed to be emitted from a light-emitting surface ofthe light guide along the longitudinal direction, and wherein the lightsources are attached to the casing, and the casing is divided intoportions in the longitudinal direction.
 2. The line-illuminating deviceaccording to claim 1, wherein the divided portions of the casing areslidably engaged with each other.
 3. A light-illuminating devicecomprising: an assembly of a casing and a transparent light guideaccommodated in the casing; and light sources provided on both ends, inthe longitudinal direction of the assembly, in which light from thelight sources is introduced into the light guide, the light is reflectedwithin the light guide and introduced in the longitudinal direction, andis allowed to be emitted from a light-emitting surface of the lightguide along the longitudinal direction, and wherein at least one of thelight sources is pressed against an end surface of the light guide withan elastic member which is formed integrally with the casing.
 4. Alight-illuminating device comprising: an assembly of a casing and atransparent light guide accommodated in the casing; and light sourcesprovided on both ends, in the longitudinal direction of the assembly inwhich light from the light sources is introduced into the light guide,the light is reflected within the light guide and introduced in thelongitudinal direction, and is allowed to be emitted from alight-emitting surface of the light guide along the longitudinaldirection, and wherein at least one of the light sources is attacheddirectly to an end surface of the light guide.
 5. An image scanningdevice comprising: a frame; the line-illuminating device according toclaim 1; a line image sensor; and a rod lens array for focusingreflected or transmitted light from a document on the line image sensor,in which the line-illuminating device, the line image sensor, and therod lens array are incorporated in the frame.
 6. An image scanningdevice comprising: a frame; the line-illuminating device according toclaim 2; a line image sensor; and a rod lens array for focusingreflected or transmitted light from a document on the line image sensor,in which the line-illuminating device, the line image sensor, and therod lens array are incorporated in the frame.
 7. An image scanningdevice comprising: a frame; the line-illuminating device according toclaim 3; a line image sensor; and a rod lens array for focusingreflected or transmitted light from a document on the line image sensor,in which the line-illuminating device, the line image sensor, and therod lens array are incorporated in the frame.
 8. An image scanningdevice comprising: a frame; the line-illuminating device according toclaim 4; a line image sensor; and a rod lens array for focusingreflected or transmitted light from a document on the line image sensor,in which the line-illuminating device, the line image sensor, and therod lens array are incorporated in the frame.
 9. The line-illuminatingdevice according to claim 1, wherein the light sources abut against endsurfaces of said light guide without gaps.
 10. The line-illuminatingdevice according to claim 1, wherein the casing and the light guide areformed of different materials, and the material of which the light guideis formed shrinks more with repeated thermal expansion and contractionthan does the material of which the casing is formed.
 11. Theline-illuminating device according to claim 3, wherein the casing andthe light guide are formed of different materials, and the material ofwhich the light guide is formed shrinks more with repeated thermalexpansion and contraction than does the material of which the casing isformed.
 12. The line-illuminating device according to claim 4, whereinthe casing and the light guide are formed of different materials, andthe material of which the light guide is formed shrinks more withrepeated thermal expansion and contraction than does the material ofwhich the casing is formed.